1. Field of the Invention
The present invention relates to a battery temperature control system in an electric automobile using a battery mounted therein as a power source, and particularly, to a battery temperature control system in an electric automobile equipped with an air-cooling and/or heating device for supplying air, which is conditioned in temperature, into a passenger compartment.
2. Description of the Prior Art
In an electric automobile, the charging of the battery is conducted when the automobile is not in use such as at night. During such charging, the battery generates heat. The battery also generates heat when it is used for driving the automobile, i.e., even during discharging. Moreover, the battery is usually accommodated in a battery chamber which is closed. For this reason, the battery may develop a considerably high temperature in some cases.
However, in such a battery used in the electric automobile, if the temperature of the battery rises above a certain temperature, e.g., 50.degree. C. or more, not only the performance of the battery but also its life-time is significantly reduced. Therefore, it is necessary to cool the battery.
Thus, it has been proposed that outside air be introduced into the battery chamber to cool the battery, as disclosed, for example, in U.S. Pat. No. 4,135,593.
However, with this system in which the battery is cooled by the outside air in the above manner, a sufficient cooling effect can not be obtained if the air temperature is high. Particularly, when a high load is applied for a long time, as is the case when the automobile travels on a long upward slope, or when a rapid charging is conducted at a charging station, the battery reaches an extremely high temperature. Therefore, the battery can not be sufficiently cooled by the outside air. As a result, the rate of discharging must be reduced, such as by slowing the vehicle, or the charging must be discontinued until the temperature of the battery declines, or the charging current must be lowered, resulting in a problem that it takes a long time to charge.
In contrast, when the temperature of the battery is lower than a predetermined temperature, the charging efficiency is low and the output of the battery is also low. When the electric automobile is used, for example, in a cold region, the temperature of the battery may not rise in some cases to a predetermined temperature during charging of thereof. In such a case, the above described prior art system in which the battery is cooled by the outside air, it is impossible to increase the temperature of the battery.
For the above-described reasons, it is necessary to maintain the temperature of the battery within a predetermined range. Particularly, in the case of a nickel-cadmium based battery having a high performance, a precise control of temperature is required.